C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Using a typedef to void for an empty parameter list produces          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Philipp Reh Guest Posted: Sun May 20, 2007 11:48 pm    Post subject: Using a typedef to void for an empty parameter list produces Dear group, I recently tried gcc-4.2 with some of my code. When compiling something that includes headers of 'devil' it complains about the following (narrowed down) case: typedef void ILvoid; ILvoid f(ILvoid); int main() { } It even fails with no arguments to g++ at all: "g++ -c myfile.cpp". The error message is: "error: '<anonymous>' has incomplete type" "error: invalid use of 'ILvoid'" for in the line delcaring f. So why should this be illegal? It just happens for the parameter type (not for the return type). Is gcc right or wrong here? Cheers, Philipp Reh -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Alberto Ganesh Barbati Guest Posted: Mon May 21, 2007 4:56 am    Post subject: Re: Using a typedef to void for an empty parameter list prod Philipp Reh ha scritto: Quote: typedef void ILvoid; ILvoid f(ILvoid); int main() { } It even fails with no arguments to g++ at all: "g++ -c myfile.cpp". The error message is: "error: '<anonymous>' has incomplete type" "error: invalid use of 'ILvoid'" for in the line delcaring f. So why should this be illegal? It just happens for the parameter type (not for the return type). Is gcc right or wrong here? I would say that the code is ill-formed and gcc is correct. The standard says in 8.3.5/2 that "The parameter list (void) is equivalent to the empty parameter list." Even if T is a typedef for void, (T), as a sequence of tokens, is not the same as (void), therefore the special case doesn't apply. HTH, Ganesh -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Mathias Gaunard Guest Posted: Mon May 21, 2007 4:58 am    Post subject: Re: Using a typedef to void for an empty parameter list pro On May 21, 1:48 am, Philipp Reh <s...@s-e-f-i.de> wrote: Quote: typedef void ILvoid; ILvoid f(ILvoid); int main() { } It even fails with no arguments to g++ at all: "g++ -c myfile.cpp". [...] So why should this be illegal? It just happens for the parameter type (not for the return type). Is gcc right or wrong here? I don't know whether it's right or wrong, but I wouldn't really expect this to work. T foo(void) is really something specific. It doesn't mean that the function takes a first argument of type void, it means it takes no argument. By the way, that feature is deprecated and only available for C compatibility. You'd better write T foo() -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Alberto Ganesh Barbati Guest Posted: Mon May 21, 2007 11:20 am    Post subject: Re: Using a typedef to void for an empty parameter list pro Mathias Gaunard ha scritto: Quote: T foo(void) is really something specific. It doesn't mean that the function takes a first argument of type void, it means it takes no argument. By the way, that feature is deprecated and only available for C compatibility. You'd better write T foo() It's true that C++ programmers are encouraged to avoid this feature, but, strictly speaking, it has not yet been formally deprecated. The list of formally deprecated features is in annex D of the standard. Ganesh -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top        C++Talk.NET Forum Index -> C++ Language (Moderated) All times are GMT Page 1 of 1 Powered by phpBB © 2001, 2006 phpBB Group